Search Results (426)

Effectively controlling the adsorption and desorption of coal and mine gas is crucial to preventing harm to the environment. Therefore, this paper investigated the adsorption of coal and methane molecules from the perspective of microscopic energy through Gaussian simulation. Gaussian 09W and GaussView 5.0 software were used to construct and optimize the molecular model of four different metamorphic coals, namely lignite, sub-bituminous coal, bituminous coal, and anthracite, and their adsorption structure with methane as well as the energy, bond length, vibration frequency, infrared spectrum, and other data on the optimal structure were obtained. The binding energy of coal molecules and methane from large to small was as follows: sub-bituminous coal (7.3696 KJ/mol), lignite (6.6149 KJ/mol), bituminous coal (5.2170 KJ/mol), and anthracite (4.9510 KJ/mol). The equilibrium distance was negatively correlated with the binding energy, and the molecular structure and position of coal largely determined the binding energy. Additionally, adsorption was more likely to occur between methane molecules and hydroxyl groups. Many new vibration modes were observed during the adsorption of coal and methane molecules. This paper is of practical significance, as studying the adsorption of coal and mine gas can prevent and control mine gas outbursts and ensure safe production. Full article

In this study, we conducted a comparative analysis of the catalytic behavior of Ni-CaO-Al₂O₃ dual functional material (DFM) and a physical mixture of Ni-Al₂O₃ and CaO-Al₂O₃ in the integrated carbon capture methanation (ICCM) process for promoted methane production. H₂-temperature-programmed surface reaction (H₂-TPSR) analysis revealed that in Ni-CaO-Al₂O₃ DFM, CO₂ adsorbed on the CaO surface can spillover to metallic Ni surface, enabling direct hydrogenation without desorption of CO₂. Ni-CaO-Al₂O₃ DFM exhibited a rapid initial methanation rate due to CO₂ spillover. The Ni-CaO-Al₂O₃ DFM, with Ni and CO₂ adsorption sites in close distance, allows efficient utilization of the heat generated by methanation to desorb strongly adsorbed CO₂, leading to enhanced methane production. Consequently, Ni-CaO-Al₂O₃ DFM produced 1.3 mmol/g_Ni of methane at 300 °C, converting 35% of the adsorbed CO₂ to methane. Full article

Injecting CO₂ into coal seams to enhance coal bed methane (ECBM) recovery has been identified as a viable method for increasing methane extraction. This process also has significant potential for sequestering large volumes of CO₂, thereby reducing the concentration of greenhouse gases in the atmosphere. However, for deep coal seams where formation pressure is relatively high, there is limited research on CO₂ injection into systems with higher methane adsorption equilibrium pressure. Existing studies, mostly confined to the low-pressure stage, fail to effectively reveal the impact of factors such as temperature, high-pressure CO₂ injection, and coal types on enhancing the recovery and sequestration of CO₂-displaced methane. Thus, this study aims to investigate the influence of temperature, pressure, and coal types on ECBM recovery and CO₂ sequestration in deep coal seams. A series of CO₂ core flooding tests were conducted on various coal cores, with CO₂ injection pressures ranging from 8 to 18 MPa. The CO₂ and methane adsorption rates, as well as methane displacement efficiency, were calculated and recorded to facilitate result interpretation. Based on the results of these physical experiments, numerical simulation was conducted to study multi-component competitive adsorption, desorption, and seepage flow under high temperature and high pressure in a deep coal seam’s horizontal well. Finally, the optimization of the total injection amount (0.7 PV) and injection pressure (approximately 15.0 MPa) was carried out for the plan of CO₂ displacement of methane in a single well in the later stage. Full article

The process of coal measure gas accumulation is relatively complex, involving multiple physicochemical processes such as migration, adsorption, desorption, and seepage of multiphase fluids (e.g., methane and water) in coal measure strata. This process is constrained by multiple factors, including geological structure, reservoir physical properties, fluid pressure, and temperature. This study used Well Z-7 in the Qinshui Basin as the research object as well as numerical simulations to reveal the processes of methane generation, migration, accumulation, and dissipation in the geological history. The results indicate that the gas content of the reservoir was basically zero in the early stage (before 25 Ma), and the gas content peaks all appeared after the peak of hydrocarbon generation (after 208 Ma). During the peak gas generation stage, the gas content increased sharply in the early stages. In the later stage, because of the pressurization of the hydrocarbon generation, the caprock broke through and was lost, and the gas content decreased in a zigzag manner. The reservoirs in the middle and upper parts of the coal measure were easily charged, which was consistent with the upward trend of diffusion and dissipation and had a certain relationship with the cumulative breakout and seepage dissipation. The gas contents of coal, shale, and tight sandstone reservoirs were positively correlated with the mature hydrocarbon generation of organic matter in coal seams, with the differences between different reservoirs gradually narrowing over time. Full article

The complex geological environment in deep layers results in differences in the pore and fracture structures and states of coalbed methane (CBM) occurrences between deep and shallow coal reservoirs. The coexistence of multiphase gases endows deep CBM with both “conventional” and “unconventional” geological attributes. Based on systematically collected coal samples from the Benxi Formation in the Daning–Jixian area of the Ordos Basin, high-pressure mercury intrusion (HPMI), low-temperature N₂ adsorption (LTN₂A), and low-pressure CO₂ adsorption (LPCO₂A) experiments were conducted to characterise the pore structures across the full pore size distribution of the Benxi Formation coals. The aim of this research is to gain an in-depth understanding of the pore size distribution of full-size pores and to explore the factors influencing their pore structure and control over the gas content in coal reservoirs. The results indicate that the pore size distribution of the coal samples from the Benxi Formation in the study area is unimodal and that nanopores are present. The pore sizes are relatively small, with an average total pore volume (PV) of 0.073 cm³/g and an average total specific surface area (SSA) of 227.87 m²/g. Among these, micropores account for 92.26% of the total PV and 99.57% of the total SSA, making micropores the primary contributors to the gas storage space in the Benxi Formation coals. Mesopores and macropores contribute relatively little to the PV and SSA, which is unfavourable for CBM permeability. The development of pores in the Benxi Formation coals in the study area is influenced by the coal maturity, vitrinite content, and ash yield. Generally, the PV increases when the coal’s rank increases; an increase in the vitrinite content promotes the development of micropores, whereas a relatively high ash yield leads to decreases in the PV and SSA. The influence of the SSAs of coal pores on the gas content is reflected mainly by its effect on the adsorbed gas content. Since adsorbed gas molecules exist mainly in coal pores in the adsorbed state, the SSAs of coal pores strongly affect the storage capacity of coal for adsorbed gas. Full article

It has been found out that Pd-Co-based catalyst, supported on anodized aluminum, possesses very high activity in combustion reactions of C₁–C₆ alkanes and toluene. The catalyst characterization has been made by N₂-pysisorption, XRD, SEM, XPS, FTIR, TEM, and EPR methods. In view of the great interest, methane combustion was investigated in detail. It is ascertained that the complete oxidation of methane proceeds by dissociative adsorption on PdO and formation of hydroxyl and methyl groups, the former being highly reactive, and it undergoes further reaction to oxygen-containing intermediates, whereupon HCHO is one of them. The presence of Co²⁺ cations promotes greatly oxygen adsorption. The dissociative adsorption is favored on neighboring Co²⁺ cations, leading to the formation of bridging peroxides. Further, the oxygen dissociates on the nearest Pd²⁺ cations. According to the results from the experimental data, instrumental methods, and the observed kinetics and DFT model calculations, it can be concluded that the reaction pathway over Pd+Co/anodic alumina support (AAS) catalyst proceeds most probably through Mars–van Krevelen. The obtained data on the kinetics were used for simulation of the methane combustion in a full-scale adiabatic reactor. Full article

Dry reforming of methane (DRM) is a promising way to convert methane and carbon dioxide into syngas, which can be further utilized to synthesize value-added chemicals. One of the main challenges for the DRM process is finding catalysts that are highly active and stable. This study explores the potential use of Ni-based catalysts modified by Ga. Different Ni-Ga/(Mg, Al)O_x catalysts, with various Ga/Ni molar ratios (0, 0.1, 0.3, 0.5, and 1), were synthesized by the co-precipitation method. The catalysts were tested for the DRM reaction to evaluate their activity and stability. The Ni/(Mg, Al)O_x and its Ga-modified Ni-Ga/(Mg, Al)O_x were characterized by N₂ adsorption–desorption, Fourier Transform Infrared Spectroscopy (FTIR), H₂-temperature-programmed reduction (TPR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Raman techniques. The test of catalytic activity, at 700 °C, 1 atm, GHSV of 42,000 mL/h/g, and a CH₄: CO₂ ratio of 1, revealed that Ga incorporation effectively enhanced the catalyst stability. Particularly, the Ni-Ga/(Mg, Al)O_x catalyst with Ga/Ni ratio of 0.3 exhibited the best catalytic performance, with CH₄ and CO₂ conversions of 66% and 74%, respectively, and an H₂/CO ratio of 0.92. Furthermore, the CH₄ and CO₂ conversions increased from 34% and 46%, respectively, when testing at 600 °C, to 94% and 96% when the catalytic activity was operated at 850 °C. The best catalyst’s 20 h stream performance demonstrated its great stability. DFT analysis revealed an alteration in the electronic properties of nickel upon Ga incorporation, the d-band center of the Ga modified catalyst (Ga/Ni ratio of 0.3) shifted closer to the Fermi level, and a charge transfer from Ga to Ni atoms was observed. This research provides valuable insights into the development of Ga-modified catalysts and emphasizes their potential for efficient conversion of greenhouse gases into syngas. Full article

Shale gas, mainly consisting of adsorbed gas and free gas, has served a critical role of supplying the growing global natural gas demand in the past decades. Considering that the adsorbed methane has contributed up to 80% of the total gas in place (GIP), understanding the methane adsorption behaviors is imperative to an accurate estimation of total GIP. Historically, the single-site Langmuir model, with the assumption of a homogeneous surface, is commonly applied to estimate the adsorbed gas amount. However, this assumption cannot depict the methane adsorption characteristics due to various compositions and pore sizes of shales. In this work, a multi-site model integrating the energetic heterogeneity in adsorption is derived to predict methane adsorption on shale. Our results show that the multi-site model is capable of addressing the heterogeneity of shales by a wide range of adsorption energy distributions (owing to the complex compositions and different pore sizes), which is different from the single-site model only characterized by single adsorption energy. Consequently, the multi-site model results have better accuracy against the experimental data. Therefore, applying the multi-site Langmuir model for estimating GIP in shales can achieve more accurate results compared with using the traditionally single-site model. Full article

The global energy market is shifting toward renewable, sustainable, and low-carbon hydrogen energy due to global environmental issues, such as rising carbon dioxide emissions, climate change, and global warming. Currently, a majority of hydrogen demands are achieved by steam methane reforming and other conventional processes, which, again, are very carbon-intensive methods, and the hydrogen produced by them needs to be purified prior to their application. Hence, researchers are continuously endeavoring to develop sustainable and efficient methods for hydrogen generation and purification. Membrane-based gas-separation technologies were proven to be more efficient than conventional technologies. This review explores the transition from conventional separation techniques, such as pressure swing adsorption and cryogenic distillation, to advanced membrane-based technologies with high selectivity and efficiency for hydrogen purification. Major emphasis is placed on various membrane materials and their corresponding membrane performance. First, we discuss various metal membranes, including dense, alloyed, and amorphous metal membranes, which exhibit high hydrogen solubility and selectivity. Further, various inorganic membranes, such as zeolites, silica, and CMSMs, are also discussed. Major emphasis is placed on the development of polymeric materials and membranes for the selective separation of hydrogen from CH₄, CO₂, and N₂. In addition, cutting-edge mixed-matrix membranes are also delineated, which involve the incorporation of inorganic fillers to improve performance. This review provides a comprehensive overview of advancements in gas-separation membranes and membrane materials in terms of hydrogen selectivity, permeability, and durability in practical applications. By analyzing various conventional and advanced technologies, this review provides a comprehensive material perspective on hydrogen separation membranes, thereby endorsing hydrogen energy for a sustainable future. Full article

Natural gas dehydration is a critical process in natural gas extraction and transportation, and the membrane separation method is the most suitable technology for gas dehydration. In this paper, based on molecular dynamics theory, we investigate the performance of a metal–organic composite membrane (ZIF-90 membrane) in natural gas dehydration. The paper elucidates the adsorption, diffusion, permeation, and separation mechanisms of water and methane with the ZIF-90 membrane, and clarifies the influence of temperature on gas separation. The results show that (1) the diffusion energy barrier and pore size are the primary factors in achieving the separation of water and methane. The diffusion energy barriers for the two molecules (CH₄ and H₂O) are ΔE(CH₄) = 155.5 meV and ΔE(H₂O) = 50.1 meV, respectively. (2) The ZIF-90 is more selective of H₂O, which is mainly due to the strong interaction between the H₂O molecule and the polar functional groups (such as aldehyde groups) within the ZIF-90. (3) A higher temperature accelerates the gas separation process. The higher the temperature is, the faster the separation process is. (4) The pore radius is identified as the intrinsic mechanism enabling the separation of water and methane in ZIF-90 membranes. Full article

The pressing environmental and energy challenges of today are driven by the depletion of fossil fuels and a surge in greenhouse gas emissions, particularly carbon dioxide. This situation highlights the critical need for sustainable energy solutions. While carbon capture and storage (CCS) technologies offer hope, they face economic challenges at the scale needed to significantly reduce carbon dioxide emissions. Biogas, produced mainly through the anaerobic digestion of various biomass sources like agricultural waste, municipal solid waste, and wastewater, presents a renewable alternative. Composed largely of methane and carbon dioxide, biogas can be upgraded to bio-methane, serving as an eco-friendly replacement for natural gas. Technological advancements, particularly in membrane separation, have made biogas purification more efficient and cost-effective. Anaerobic digestion, a key process in biogas production, breaks down organic matter into simpler compounds, which are then transformed into gases like methane and carbon dioxide. The composition of biogas depends on the feedstock and digestion conditions, with methane being a valuable but challenging component to separate due to its greenhouse gas properties. Several purification technologies have been developed, including absorption, adsorption, cryogenic separation, and membrane separation, each with unique benefits and drawbacks. Membrane separation is particularly promising for its environmental benefits and scalability. However, the biogas industry faces challenges, especially in developing countries, due to high costs and limited research and development. Overcoming these obstacles requires collaboration among various stakeholders. Looking ahead, the future of biogas technology is bright, with advances in membrane materials and integrated refining processes. Integrating biogas into sectors like waste management and agriculture is crucial for its development and for meeting global renewable energy goals. Biogas technology not only reduces dependence on fossil fuels but also plays a vital role in the transition to sustainable energy. Full article

This study investigates the impact of kaolin and boehmite alumina binders on the synthesis, catalytic properties, and attrition resistance of a La_0.7Sr_0.3FeO₃ (LSF) perovskite catalyst designed for the chemical looping partial oxidation (CLPO) of methane to produce synthesis gas sustainably. The as-synthesized and used catalysts with varying kaolin and boehmite alumina contents (KB_(x,y)/LSF) were scrutinized by a variety of characterization methods, including XRD, FE-SEM/EDS, BET, TPD-NH₃, and TPD-O₂ techniques. The catalytic activity of the synthesized samples was tested at 800 to 900 °C in a fixed-bed reactor producing syngas through the CLPO process over the consecutive redox cycles. Additionally, the attrition resistance of the fresh and used catalyst samples was examined in a jet cup apparatus to assess their durability against the stresses induced by thermal shocks or changes in the crystal lattice caused by chemical reactions. The characterization results showed the pure perovskite crystal structure of KB_(x,y)/LSF catalysts demonstrating adequate oxygen adsorption capacity, effective coke mitigation capability, robust thermal stability, and resilience to agglomeration during repetitive redox cycles. Among the tested catalysts, KB_(25,15)/LSF was identified as the superior sample, as it could consistently produce syngas with a suitable H₂:CO molar ratio varying from 2 to 3 within ten redox cycles at 900 °C, with CH₄ conversion and CO selectivity values up to 64% and 87%, respectively. The synthesized catalysts demonstrated a logarithmic attrition pattern in the jet cup tests at room temperature, featuring high attrition resistance after the erosion of particle shape irregularities or weakly bound particles. Moreover, the KB_(25,15)/LSF catalyst used at 900 °C showed great resistance in the attrition test, warranting its endurance in the face of extraordinarily harsh conditions in fluidized bed reactors employed for the CLPO process. Full article

The pore fracture structure of deep coal reservoirs is crucial for evaluating the potential of deep coalbed methane resources, conducting exploration and development, and controlling coal mine gas disasters. Mercury intrusion porosimetry, the liquid nitrogen method, and the low-temperature carbon dioxide adsorption method were used to study the full pore size structure and pore fractal characteristics of different coal grades in deep coal and comprehensively characterize the pore structure of kilometer-level coal mining. The sponge, Frenkel–Halsey–Hill (FHH), and density function models were applied to comprehensively analyze the pore complexity of coal, and the influence of metamorphic degree on pore size structure was evaluated. The distribution relationship of pore volume in different stages of coal samples was macropore→mesopore→micropore, and macropores had the best connectivity. Micropores and mesopores had the largest specific surface area, and the development of micropores and microcracks controlled the deep gas adsorption performance. The micropore volume and specific surface area both revealed a nonlinear decreasing trend with the increase in volatile matter, and coal metamorphism promoted the development of micropores. The pore volume and specific surface area of mesopores and macropores decreased first and then increased in a “U” shape with increasing volatile matter. In contrast, the fractal dimension D₁ revealed an inverted U shape with increasing volatile matter, followed by a decrease. The D₂ value decreased nonlinearly with increasing volatile matter, whereas the D₃ value increased nonlinearly with increasing volatile matter. The degree of metamorphism increased, and the microporous structure became more regular. Full article

A series of M(x)CoCeMgAlO mixed oxides with different transition metals (M = Cu, Fe, Mn, and Ni) with an M content x = 3 at. %, and another series of Fe(x)CoCeMgAlO mixed oxides with Fe contents x ranging from 1 to 9 at. % with respect to cations, while keeping constant in both cases 40 at. % Co, 10 at. % Ce and Mg/Al atomic ratio of 3 were prepared via thermal decomposition at 750 °C in air of their corresponding layered double hydroxide (LDH) precursors obtained by coprecipitation. They were tested in a fixed bed reactor for complete methane oxidation with a gas feed of 1 vol.% methane in air to evaluate their catalytic performance. The physico-structural properties of the mixed oxide samples were investigated with several techniques, such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), elemental mappings, inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction under hydrogen (H₂-TPR) and nitrogen adsorption–desorption at −196 °C. XRD analysis revealed in all the samples the presence of Co₃O₄ crystallites together with periclase-like and CeO₂ phases, with no separate M-based oxide phase. All the cations were distributed homogeneously, as suggested by EDX measurements and elemental mappings of the samples. The metal contents, determined by EDX and ICP-OES, were in accordance with the theoretical values set for the catalysts’ preparation. The redox properties studied by H₂-TPR, along with the surface composition determined by XPS, provided information to elucidate the catalytic combustion properties of the studied mixed oxide materials. The methane combustion tests showed that all the M-promoted CoCeMgAlO mixed oxides were more active than the M-free counterpart, the highest promoting effect being observed for Fe as the doping transition metal. The Fe(x)CoCeMgAlO mixed oxide sample, with x = 3 at. % Fe displayed the highest catalytic activity for methane combustion with a temperature corresponding to 50% methane conversion, T₅₀, of 489 °C, which is ca. 40 °C lower than that of the unpromoted catalyst. This was attributed to its superior redox properties and lowest activation energy among the studied catalysts, likely due to a Fe–Co–Ce synergistic interaction. In addition, long-term tests of Fe(3)CoCeMgAlO mixed oxide were performed, showing good stability over 60 h on-stream. On the other hand, the addition of water vapors in the feed led to textural and structural changes in the Fe(3)CoCeMgAlO system, affecting its catalytic performance in methane complete oxidation. At the same time, the catalyst showed relatively good recovery of its catalytic activity as soon as the water vapors were removed from the feed. Full article

Given that methane (CH₄) and nitrogen (N₂) have similar properties, achieving high-purity enrichment of CH₄ from nitrogen-rich low-grade gas is extremely challenging and is of great significance for sustainable development in energy and the environment. This paper reviews the research progress on carbon-based materials, zeolites, and MOFs as adsorbent materials for CH₄/N₂ separation. It focuses on the relationship between the composition, pore size, surface chemistry of the adsorbents, CH₄/N₂ selectivity, and CH₄ adsorption capacity. The paper also highlights that controlling pore size and atomic-scale composition and optimizing these features for the best match are key directions for the development of new adsorbents. Additionally, it points out that MOFs, which combine the advantages of carbon-based adsorbents and zeolites, are likely to become the most promising adsorbent materials for efficient CH₄/N₂ separation. Full article